Semiconductor light-emitting devices including light emitting diodes (LEDs), resonant cavity light emitting diodes (RCLEDs), vertical cavity laser diodes (VCSELs), and edge emitting lasers are among the most efficient light sources currently available. Materials systems currently of interest in the manufacture of high-brightness light emitting devices capable of operation across the visible spectrum include Group III-V semiconductors, particularly binary, ternary, and quaternary alloys of gallium, aluminum, indium, and nitrogen, also referred to as III-nitride materials. Typically, III-nitride light emitting devices are fabricated by epitaxially growing a stack of semiconductor layers of different compositions and dopant concentrations on a sapphire, silicon carbide, III-nitride, or other suitable substrate by metal-organic chemical vapor deposition (MOCVD), molecular beam epitaxy (MBE), or other epitaxial techniques. The stack often includes one or more n-type layers doped with, for example, Si, formed over the substrate, one or more light emitting layers in an active region formed over the n-type layer or layers, and one or more p-type layers doped with, for example, Mg, formed over the active region. Electrical contacts are formed on the n- and p-type regions.
FIG. 1 illustrates a known LED. After growth of the epitaxial structure on the growth substrate 2, metal contacts are formed on the epitaxial structure, and the device is flipped over relative to the growth direction and attached to a mount 5. In FIG. 1, the epitaxial structure and metal contacts are shown as block 3. A phosphor layer 4 is formed over the substrate 2. Phosphor layer 4 absorbs light emitted by the light emitting layer of the epitaxial structure and emits light of a different wavelength. A lens 6 is disposed over the LED and the mount 5.
In the device illustrated in FIG. 1, a majority of the light extracted from the LED is extracted from the substrate side (as opposed to the epitaxial structure side). Light emitted by the light emitting layer toward the metal contacts may be partially reflected by a reflective p-contact, before exiting the structure. The p-contact may cover some portion of the epitaxial structure surface opposite the substrate. The phosphor generally emits light in all directions. Some light 8 absorbed by the phosphor and emitted at a different wavelength is emitted in the direction of lens 6. Some light 9 emitted by the phosphor is emitted back toward the epitaxial structure 3. Because the epitaxial structure 3 is not very reflective, light 9 is likely to be absorbed, which reduces the efficiency of the device of FIG. 1.